Automatic protective circuit breaker

ABSTRACT

A rapid-action, current-limiting automatic switch with a magnetic tripping device with an iron circuit of small geometric dimensions and few ampere turns of the exciter coil required to make the armature acting on the latching mechanism respond, comprises an additional armature which acts on a movable contact member and is arranged in a magnetic circuit which is in common with the first armature. The tripping device contains a magnetic core, an exciter coil and a magnetic shunt across the air gap of the additional armature.

United States Patent [1 1 Drubig Oct. 21, 1975 [5 AUTOMATIC PROTECTIVE CIRCUIT 3,569,879 3/1971 Gryctko 335/265 BREAKER 3,588,762 6/1971 Willard 335 16 3,588,763 6/197] Heft 335/16 [75] Inventor: Horst Drubig, Regensburg,

G I ermany Primary Examiner-Harold Broome [73] Ass1gnee: Siemens Aktiengesellschaft, Munich, Attorney, Agent, or Firml(enyon & Kenyon Reilly Germany Carr & Chapin [22] Filed: Sept. 19, 1974 [21] App]. N0.: 507,572 [57] ABSTRACT A rapid-action, current-limiting automatic switch with [30] Foreign Application Priority Data a magnetic tri in device with an iron circuit of small PP Sept. 27, 1973 Germany 2348613 geometric dimenslohs and few ampere turns of the citer coil required to make the armature acting on the 52 U.S. c1. 335/14; 335/236; 335/265 latching mechanism respond, comprises an additional 51 11m.c1. H01H 75/10; HOlH 77/06 armature which acts on a movable Contact member 53 Field f Search 335 14 1 23 2 5 174 and is arranged in a magnetic circuit which is in com- 335/175 6, 1 76 mon with the first armature. The tripping device contains a magnetic core, an exciter coil and a magnetic 5 References Cited shunt across the air gap of the additional armature.

UNITED STATES PATENTS 13 Claims, 13 Drawing Figures 2,55l,303 5/1951 Theunissen 335/265 US. Patent Oct. 21, 1975 SheetlofS 3,914,720

US. Patent Oct. 21, 1975 Sheet3of5 3,914,720

US. Patent Oct. 21, 1975 Sheet5of5 3,914,720

1 AUTOMATIC PROTECTHVE CIRCUIT BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention The invention concerns an automatic switch, particularly a protective circuit breaker, with a latching mechanism and a magnetic tripping device which comprises two armatures which are placed, together with their operating air gaps, in a common magnetic circuit of said magnetic tripping device, containing a magnetic core with an exciter coil and, as the case may be, a magnetic yoke, the first of which armatures acts on an unlatching lever of the latching mechanism and the second on a movable contact member, particularly on a movable contact member that can be actuated by the latching mechanism.

2. Description of the Prior Art Such an automatic switch is known from the German Pat. No. 2,115,030. The armature acting on the unlatching lever of the latching mechanism is a hinged armature, while the armature acting on the movable contact element is a plunger-type armature. Parallel to the operating air gap of the hinged armature is disposed a shunt body which consists of magnetic material and which causes the magnetic flux, with rising current in the exciter coil of the magnetic tripping device, to go at first via the operating air gap of the plunger-type armature and the magnetic shunt body which is in series with this operating air gap. Only after the magnetic shunt body is saturated does sufficient magnetic flux go through the operating air gap of the hinged armature that the latter is pulled up and the latching mechanism releases. As the magnetic flux permeating the shunt body also passes through the operating air gap of the plunger-type armature acting on the movable contact member, the response current of the plunger-type armature acting on the movable contact member is smaller than the response current of the hinged armature acting on the unlatching lever of the latching mechanism. This means, however, that the plungertype armature responds prior to the hinged armature and acts on the movable contact member before theh latching mechanism is unlatched. Thus, it is necessary for the proper functioning of an automatic switch that the response current of the armature unlatching the latching mechanism is smaller than the response current of the armature that acts directly on a movable contact member in the opening sense. In the known automatic switch, this can be accomplished only if the plunger-type armature is restrained particularly strongly. This strong restraining of the plunger-type armature, however, has the effect that it can be made to respond only under the action of considerable magnetic forces.

The number of ampere turns of the exciter coil of the magnetic tripping device required for releasing the latching mechanism is given by that number of ampere turns which, overcoming the air gap of the plunger-type armature, saturates the shunt body, plus the number of ampere turns which, overcoming the air gap of the plunger-type armature and the air gap of the hinged armature, imparts to the hinged armature the force required for releasing the latching mechanism. Additional ampere turns are required to overcome the strong restraining force at the plunger-type armature and to achieve a sufficiently high opening velocity and opening force of the plunger-type armature. For these reasons, large geometric dimensions of the iron circuit of the magnetic tripping device and therefore, also large dimensions of the automatic switch are required, besides the large number of ampere turns, in the known automatic switch, in order to obtain a sufficiently large force of the plunger-type armature.

Because of the required large geometric dimensions (cross section) of the iron circuit of the magnetic tripping device and the required large force of the plungertype armature, the magnetic force acting on the hinged armature furthermore continues to rise quadratically in the prior art automatic switch for currents that are larger than the response current of this hinged armature. For this reason, this automatic switch is particularly sensitive to short current pulses, e.g., switching pulses of incandescent lamp or fluorescent lamp groups with capacitive compensation, which cause the automatic switch to trip in an undesired manner, if these current pulses exceed even slightly the response current of the hinged armature. Because of this high pulse sensitivity, the prior art automatic switch has only very little or practically no selectivity with respect to a following, current-limiting automatic switch.

From the published documentation for the German Design Pat. No. 1,798,768, a prior art automatic switch is shown with a magnetic tripping device, in which an iron strip is disposed parallel to the air gap between the magnetic core and a plunger-type armature striking the contact members directly. However, the magnetic tripping device comprises no additional armature which acts on the unlatching lever of a latching mechanism, and the iron strip serves only to transmit a sufficiently strong magnetic stray field to the arc gap which is thereby blasted when the contact members are opened for interrupting small d-c currents. The iron strip, particularly its cross section, is therefore designed so that it is saturated with certainty for currents appreciably below the response current of the magnetic tripping device.

There are safety specifications for automatic switches which concerns a tolerance range for the response current of the magnetic tripping device. This tolerance range which is caused e.g. by the possible phase shifts and forms of the oscillating current and by the mechanical properties of the automatic switch must be within predetermined limits.

If the upper limit is exceeded, the automatic switch must always trip, while it must not trip below the lower limit. According to the terminology accepted by the technical community (see, for instance, AEG-Manual 1, Fundamentals of Electrical Engineering, Elitera- Verlag Berlin 1972, particularly page 192, left column, lines 5 to 7), a magnetic material goes into magnetic saturation if its permeability p. p #0 (u, relative permeability, y. magnetic field constant or induction constant), starting from a maximum value, no longer increases, but decreases with increasing magnetic excitation or magnetic field strength. The magnetic material is magnetically saturated if the relative permeability n, has finally fallen to the constant value 1 with increasing magnetic excitation or field strength.

It ist an object of this invention to avoid said heavy restraint of the armature acting on the movable contact member and to keep the geometric dimensions of the iron circuit small and to reduce the number of ampere turns of the exciter coil of the magnetic tripping device required to make the armature acting on the latching mechanism respond.

SUMMARY OF THE INVENTION To solve this problem, an automatic switch of the kind mentioned at the outset is characterized, according to the invention, by the feature that parallel to the operating air gap of the second armature, which acts on the movable contact member, a magnetic shunt is disposed which magnetically bridges this operating air gap at least partly.

With increasing overcurrents in the exciter coil of the magnetic tripping device, the magnetic flux permeates first the magnetic shunt which is disposed parallel to the operating air gap of the armature acting on the movable contact member, and at the same time the operating air gap, disposed in series with this shunt, of the first armature, which acts on the unlatching lever of the latching mechanism. The number of ampere turns required to make the armature acting on the latching mechanism respond is therefore given, up to the point of magnetic saturation of the shunt, only by the operating air gap of the first armature, which acts on the unlatching lever of the latching mechanism. From the values of the overcurrents on, at which the shunt goes into magnetic saturation, the operating air gap of the secnd armature, which acts directly onthe movable contact member, is either in series or parallel with the operating air gap of the first armature so that a force effect takes place in it only from these over-currents In spite of the small geometric dimensions of the iron circuit and the small number of ampere turns of the exciter coil of the magnetic tripping device required to make the armature acting on the latching mechanism respond, the automatic switch according to the invention is a fast-action switch, which can be designed as a current-limiting switch without difficulty.

The shunt which is parallel to the operating air gap of the second armature, which acts on the movable contact member, is advantageously designed so that it goes into magnetic saturation, or is just magnetically saturated, at the peak value of a current which flows through the exciter coil of the magnetic tripping device and is within the tolerance of the response current of the first armature, which acts on the unlatching lever of the magnetic tripping device. Thereby, practically no restraint, or perhaps only a weak fixation, for instance, through a weak and soft spring, is necessary for the armature acting on the movable contact member. It is furthermore achieved thereby that the force of the armature acting on the latching mechanism no longer continues to increase quadratically above its response value. Therefore, the armature acting on the unlatching lever of the latching mechanism is particularly insensitive to energization of the exciter coil of the magnetic tripping device by pulse-like currents (selectivity). The tolerance range of the response current is given by the different possible phase positions of the current waves, by the waveform of these current waves, and by the mechanical properties of the automatic switch, among others.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 show embodiments of magnetic tripping devices of an automatic switch according to the invention.

FIGS. 3 and 4 show equivalent magnetic circuit,diagrams for the magnetic tripping devices according to FIGS. 1 and 2.

FIG. 5 shows the curve of the magnetic induction in the air gaps of the armatures of the magnetic tripping devices according to FIGS. 1 and 2.

FIG. 6 shows the curve of the force at the armatures of the magnetic tripping device according to FIGS. 1 and 2.

FIGS. 7 and 8 show a different embodiment of magnetic tripping devices of an automatic switch according to the invention.

FIGS. 9 and 10 show equivalent magnetic circuit diagrams for the magnetic tripping devices according to FIGS. 7 and 8.

FIG. 11 shows the curve of the magnetic inductions in the air gaps of the armatures of the magnetic tripping devices according to FIGS. 7 and 8.

FIG. 12 shows the curve of the forces on the armature of the magnetic tripping devices according to FIGS. 7 and 8.

FIG. 13 shows a multi-pole automatic switch connected from single-pole automatic switches in accordance with the invention.

DESCRIPTION OF THE INVENTION In FIGS. 1 and 2, magnetic tripping devices with a magnetic core 1 consisting of iron are shown. These magnetic tripping devices further comprise U-shaped magnetic yokes 2 of magnetic material, e.g., iron, which establish a magnetic connection between the magnetic core 1 and the two plunger-type armatures 3 and 4. These plunger-type armatures 3 and 4 are nested coaxially inside each other. They are both arranged coaxially in a guide tube 6 of nonmagnetic material, for example, of brass. The magnetic core 1 is also placed within this guide tube. An exciter coil 5 is mounted on the outer cylinder surface of the guide tube 6.

In the magnetic tripping device according to FIG. 1, the plunger-type armature 3 acting on the unlatching lever 7 of the latching mechanism 8 is arranged inside the striking armature, which is designed as a cylindrical plunger armature 4. This armature 4 acts by means of mechanical linkage on the movable contact member 9.

In the magnetic tripping device according to FIG. 2, the striking armature, which acts directly on the movable contact member 9 and is designed as a plungertype armature, is placed inside of the plunger-type armature 3, which is designed as a hollow cylinder and acts on the unlatching lever 7 of the latching mechanism 8. The plunger-type armature 4 of the magnetic tripping device according to FIG. 2 is provided with a push rod 4a of nonmagnetic material, which is coaxial to the guide tube 6 and is free to move within the magnet core 1 which is designed in the shape of a hollow cylinder. Push rod 4a strikes movable contact member 9 of the protective circuit breaker when the plunger armature 4 responds. In the rest position of both annatures of the magnetic tripping devices according to FIGS. 1 and 2, the air gap (operating air gap) between the magnetic core 1 and the plunger armature 4, which acts directly on the movable contact member 9, has a greater length 6 than the length 8 of the air gap (operating air gap) between the magnetic core 1 and the plunger-type armature 3 acting on the unlatching 7.

In the magnetic tripping devices according to FIGS.

-1 and 2, the plunger-type armature 3, which acts on the unlatching lever 7 of the latching mechanism 8, acts as a magnetic shunt body which is parallel to the operating air gap between the magnetic core 1 and the plunger armature 3. This magnetic shunt body bridges the operating air gap between the magnetic core I and the plunger armature '4 and goes into magnetic saturation in the case of overcurrents or short-circuit currents which flow through the exciter coil and lie within the tolerance range of the response current of the armature 3.

If the armature 3, is magnetically unsaturated, i.e., if the magnetic shunt body at the air gap 0 is unsaturated, the equivalent magnetic circuit diagram according to FIG. 3 applies to the magnetic tripping devices according to FIGS. 1 and 2. The magnetic reluctance R 5 and R 5 of the initial air gaps (operating air gaps) between the magnetic core 1 on the one hand and the armature 3 and the armature 4, respectively, are connected in parallel by means of symbolic switches S1 and S2. The symbolic switch S1, which lies in the branch of the magnetic reluctance R 5 of the operating air gap between the magnetic core land the armature 3, bridges a magnetic reluctance R 5 2 5 by which the magnetic reluctance R 5 D of the operating air gap 61 between-the magnetic core I and the armature 3 increases if the armature 3 is magnetically saturated. B is the magnetic flux generated by the exciter coil 5. In FIGS. 3 and 4 the motion air gaps between the magnetic yokes 2 and the two plunger-type armatures 3 and 4, which are very short and of large area, are not taken into account, as they do not influence in principle the behavior of the magnetic tripping device according to FIGS. 1 and 2.

As will be seen from FIG. 3, the symbolic switch S1 is closed if the magnetic shunt to the operating air gap between the magnetic core and the armature 4 with the initial length 0 which is formed by the armature 3, is unsaturated, and the symbolic switch S2 is open. In other words if the iron of the armature 3 is unsaturated, the magnetic flux caused by the magnetic flux of the exciter coil 5 travels almost exclusively by means of the operating air gap between the magnetic core 1 and the armature 3, which has the initial length 6 If the iron of the armature 3 and therefore, the magnetic shunt to the operating air gap between the magnetic core 1 and the armature 4, is magnetically saturated, the equivalent magnetic circuit diagram according to FIG. 4 applies, in which the symbolic switch S1 is open and the symbolic switch S2 is closed. Thereby, an additional magnetic reluctance R 5 2 5 is connected in series to the magnetic reluctance R 5 of the operating air gap between the magnetic core 1 and the armature 3. The sum of these two magnetic reluctances corresponds to an air gap between the magnetic core 1 and the armature 4, which has the same cross section as the armature 3. Because of the closed symbolic switch S2, the magnetic reluctance of the operating air gap between the magnetic core 1 and the armature 4, which has the same cross section as the armature 4 has the initial length 8,, is connected parallel to these two seriesconnected magnetic reluctances. In the case of FIG. 1, the cross section of the armature 4 is annular, and in the case of FIG. 2, the cross section of armature 3 is annular.

In FIG. 5, the magnetic induction B in the operating air gap between the magnetic core 1 and the armature 3 and the magnetic induction 8, in the operating air gap between the magnetic the magnetic core 1 and the armature 4 of the magnetic tripping devices according to FIGS. 1 and 2 are plotted versus the peak value of the magnetic excitation H w (ampere turns), where I= peak value of the current. For simplification, the magnetic excitation required for saturating the iron of the arrnatures 3 and 4 is assumed as zero. As will be seen, the induction B in the operating air gap between the magnetic core 1 and the armature 4 is zero as long as the iron of the armature 3 is unsaturated. Only when the iron of the armature 3 is magnetically saturated does the magnetic induction B in the operating air gap between the magnetic core 1 and the armature 4 increase.

As shown in FIG. 6, where the magnetic force F acting on the armature is plotted versus the peak value of the magnetic excitation H w (ampere turns), the magnetic force F, acting on the armature 3 increases quadratically very quickly up to the saturation of the iron of the armature 3 and subsequently rises linearly with only a slight slope as the magnetic excitation increases. Only after the iron of the armature 3 is saturated does a magnetic force F occur at the armature 4. The armature 3 is advantageously designed so that it goes into magnetic saturation or is just magnetically saturated at the peak value of a current which flows through the exciter coil 5 of the magnetic tripping device and lies within the tolerance range N/ 2 w of the response current of this armature 3.

If a short-circuit current of the magnitude of the response current of the armature 3, which acts on the unlatching lever 7 of the latching mechanism 8, flows through the exciter coil '5, the magnetic force F acting on the armature 3 increases quadratically, as FIG. 6 shows, and, after several half-cycles, generally causes the latching mechanism to unlatch. If a current pulse of the duration of an a-c half-cycle or less occurs in the exciter coil 5, only a small increase of the force is ac-' complished by the current component which exceeds the tolerance range N/ VT. w of the response current of the armature 3, which is given by the approximately linear increase of the force F,, so that the unlatching takes place only at current pulses which are appreciably larger than the response current of the unlatching armature. In both cases of unlatching, the latching mechanism 8 is released and the movable contact member 9 is moved away from the stationary contact member 10 in the direction of the arrow 90. For larger short-circuit currents, also the magnetic force F exerted on the armature 4 increases quadratically, as FIG. 6 shows, after the magnetic saturation of the iron of the armature 3 occurs. The restoring force of the relatively weak fixation spring 13 of the armature 4 is quickly overcome, and the armature 4 is accelerated more and more as the length of the air gap between it and the gap between it and the magnetic core 1 decreases. Particularly with these large short-circuit currents, the motion of the armature 4 can proceed entirely independently of the motion of the armature 3. Both courses of movement depend only on the magnitude of the'magnetic force and the mass to be accelerated, and if the shortcircuit currents are substantially above the response current, it is entirely permissible and even desirable that with appropriate matching of magnetic forces and the armature masses, the armature 4 acting as a striking armature opens the movable contact member 9, which can be operated by the latching mechanism 8, immediately, before the latching mechanism 8 is u nlatched. As arising force also acts on the plunger-type armature 3, which is associated with the unlatching lever 7, the unlatching of the latching mechanism is effected in such a case in fractions of a millisecond after the opening of the contact by the armature ;4, without the occurrence of pumping of the armature 4 on the movable contact member 9, which is not released by the latching mechanism. The fast'opening of the contact gap which thus occurs in case of large short-circuit currents, brings about the current limitation, in conjunction with a sufficiently high are voltage, and thereby, the high switching capacity.

An automatic switch in accordance with the invention with a magnetic tripping device according to FIGS. 1 and 2 has, in particular, the advantage that for the at: mature 3, which acts on the unlatching lever 7, only an air gap to the magnetic core 1- is necessary, which has a relatively short length. This air gap length is determined only by the geometric design of the latching mechanism 8, i.e., by the release travel of the latch lever 7. The nominal response current for the automaticswitch therefore needs to supply only a magnetic excitation, which is determined by the required, relatively small air gap between the magnetic core 1 and the armature 3 associated with the unlatching lever 7 and perhaps further by the unlatching force of the latching mechanism 8. The air gap. between the magnetic core 1 and the striking armature 4 acting directly on the movable contact member 9 is of no importance for the design of the dimensions of the magnetic tripping device, as far as the armature 3 associated with the unlatching lever 7 is concerned. This air gap can have, in particular, a relatively great length, so that it strikes, after a long running start, the movable contact member 9 with .very high-momentum andvelocity and thereby imparts to ita very high opening velocity. In spite of the large air gap between the magnetic core 1 and the armature 4 (striking armature) which strikes the movable contact member 9 directly, the design of theunlatching portion of the magnetic tripping device according to FIGS. 1 and 2, associated with the unlatching lever 7, is not affected in view of the response current of the armature '3, Moreover, practically no restraining of the armature 4, which acts directly on the movable contact,

member 9, is necessary, as a force effect occurs in it only if the current flowing through they exciter coil has reached approximately the value of the response current of the armature 3. In general, however, one will providea weak restraining spring 13, which fixes .the armature 4, in the starting position shown in FIGS. 1

and 2.

As according to FIG. 6, only a rather small increase of the force action on the armature 3 results for currents in the exciter coil 5 which exceed the responsein a time shorter than the half-cycle of the ac. current current of the armature 3, according to the approximately linear branch of the curve P an automatic switch according to the invention is very insensitiveto short current pulse, e.g., switching pulses, and is therefore particularly well suited, without reduction of the.

circuit, so that only asingle current pulse acts on the magnetic tripping device of the preceding power circuit breaken-If this preceding power circuit breaker is an automatic switch according to the invention, it is considerably less sensitive to this single current pulse than prior art automaticswitches and therefore trips only at considerably larger uninfluenced short-circuit currents than prior automatic switches, so that thus a considerable increase of the selectivity is achieved.

Automatic switches according to the invention with magnetic tripping devicesshown in FIGS. 7 and 8 have thesame advantages. In, the switch according to FIG. 7,-the magnetic shunt is formed by an immovable body of-magnetic material 1 which is placed in the magnetic circuit of the magnetic tripping device. This body of magnetic material consists of a hollow cylinder 15, which at one endface joins'the magnetic core 1 of the magnetic tripping device. In this hollow cylinder 15, a likewise cylindrical plunger-type armature 4 of magnetic material is arranged, which acts directly on the movable contact member 9 by means of a nonmagnetic push-rod 4a. The hollow cylinder completely bridges, as a magnetic shunt, the operating air gap between the plungenarmature 4 and the magnetic core 1. The exciter coil5 is mounted on the magnetic core and the hollow cylinder 15. At an angled-off magnetic yoke 2 is attached a hingedarmature 3, which acts on the unlatching lever 7 of the latching mechanism ,8 and which is arranged opposite the pole surface la of themagnetic .core. The push rod 4a is brought concentrically through the magnetic core 1. The magnetic core 1, together with the'hollow cylinder 15, the magnetic yoke 2 and the hinged armature3 form a closed magnetic circuit. ,A restoring spring 14 is associated with .the

hinged armature 3, while the plunger armature 4 has a face, both of which consist of magnetic material. The Y armature 3 acting on the unlatching, lever 7v of the latching mechanism 8 consists of a plate of magnetic material which is guided in a guide 16 and is provided with a restoring spring 14. The exciter coil 5 is mounted on a cylinder of non-magnetic material 6, in which the magnetic core 1 and the post lb are arranged coaxially.

The exciter coil 5 is secured in a magnetic yoke 2 con-.

sisting of a double angle by an annular washer 17 of non-magnetic material. The armature which acts directly onithe movable contact member 9 is designed as a plunger armature 4, which is arranged coaxially in the insulating material sleeve 6 and has a central coaxial hole 4a to receive the post lb. This immovable post 1b forms amagn'etic shunt to the air gap between the mag- -rent of the hinged armature 3.

As the equivalent magnetic circuit diagram according to FIG. 9 shows, in-which B is the magnetic excitation caused by the exciter coil 5, R represents the magnetic reluctance of the air gap between the magnetic core 1 and the armature 4, and R 5 represents the magnetic reluctance of the air gap between the hinged armature 3 and the magnetic core 1. S1, a symbolic switch which is closed if the hollow cylinder or the post 1b, respectively, is magnetically unsaturated, is open if the hollow cylinder 15 or the post lb is magnetically saturated. The air gap between the magnetic core 1 and the plunger armature 4 is at first not effective when the cylinder 15 or the post lb is magnetically unsaturated, i.e., if the symbolic switch S1 is closed. Only-the operating air gap of the initial length 8 between the hinged armature 3 and the magnetic core 1 is effective. As shown in FIG. 10, the symbolic switch S1 is open if the hollow cylinder 15 or the post lb is magnetically saturated, and the magnetic reluctance of the air gap with the initial length 8 between the magnetic core 1 and the plunger armature 4 is connected in series with'the magnetic reluctance of the air gap with the initial length 6 between the hinged armature 3 and the magnetic core 1.

As shown in FIG.'11, in which the flux B, in the air gap between the armature 3 and the magnetic core 1 and the flux B in the air gap between the armature 4 and the magnetic excitation H w (ampere turns) for the magnetic tripping devices according to FIGS. 7 and and 8. The increase of the flux B, in the air gap between the' armature 3 and the magnetic core 1 is given I only by the length of this air gap. The magnetic saturation of the iron in the hollow cylinder 15 or the post lb is given by the ratio of the areas, (A,'- A A,, which for FIG. 11 is assumed as approximately 1:2, and where A is the cross-section area of the armature 4. Therefore, the curve of the induction in the air gap between through the exciter coil 5 a magnetic flux which is about 50 percent of the saturation induction. Only from this current on, an increase in the induction occurs for the flux B in the air gap with the initial length 6, between the magnetic core 1 and the armature 4.

FIG. 12 shows, plot ed versus the peak value of the magnetic excitation w I (ampere turns), the curves of the magnetic forces F and F exerted on the armatures 3 and 4,-resulting therefrom. The tolerance range N/ T. w for the response current of the armature 3 flowing through the exciter coil 5 occurs about in the region of the discontinuity of the force curve F for the armature 3 acting on the unlatching lever 7 of the latching mechanism 8. This insures that a magnetic force is exerted on the armature 4, which acts directly on the movable contact member, only if the tolerance range of the response current of the armature 3 is exceeded in the case of small overload or short-circuit currents.

In a magnetic tripping device of an automatic switch which is opposite the armature acting on the unlatching lever of the latching mechanism, the length of the air gap between the armature acting on the unlatching lever and the magnetic core can be increased for part of this end face and the induction curve and the magnetic force, which is exerted on the armature associated with the unlatching lever can thereby be varied.

An automatic switch according to the invention has, in particular, the advantage that the air gap of the striking armature acting directly on the movable contact member and therefore, also the contact burn-off, for instance, and the manufacturing tolerances have no effect of any kind on the number of ampere turns, required for the function of the armature acting on the unlatching leverof the latching mechanism, of the exciter coil'of the magnetic tripping'device for unlatching the latching mechanism.

Further, as FIG. l3 shows, the invention concerns not only single-pole automatic switches with a single latching mechanism and a single magnetic tripping device, but also multi-pole automatic switches with at least one movable contact member per pole. A single latching mechanism or one latching mechanism per pole and one magnetic tripping device per pole can be designed in accordance with the invention. This can involve line protection switches, power circuit breakers and motor protection switches. It is particularly advantageous to design a three-phase power circuit breaker in accordance with the invention and to associate with each of the three phases a movable contact member 39 and a magnetic tripping device. Each of the three magnetic tripping devices has a release armature 33, which serves for releasing the single latching mechanisms 38 of the three-phase power circuit and acts on the unlatching lever 37 of this latching mechanism 38. The three release armatures 33 are restrained by a common spring 44, so that the sum of the forces of the three release armatures 33 acts on this spring 44. Each of the three magnetic tripping devices has furthermore a second striking armature 34 acting on the movable contact member 39 associated with it, with a magnetic shunt 45 to the air gap, designed in accordance with the invention. This three-phase power circuit breaker has further improved selectivity properties over a current-limiting power circuit breaker in accordance with the German Pat. No. 1,588,109. With it, values of selectivity are achieved which are practically equal to those obtained with three-phase power circuit breakers with timedelayed magnetic tripping devices. The striking armatures 34 acting on the movable contact members 39 are in no way influenced by the coupling of the three release armatures 33 acting on the unlatching lever 37 of the latching mechanism 38, so that a three-phase power circuit breaker designed in accordance with the invention has a high switching capacity and is currentlimiting. The three release armatures 33 can advantageously be rigidly coupled with each other by means of connecting members, or also rest against the unlatching lever 37 of the latching mechanism 38 independently of each other. The three striking armatures 34 can also be coupled with each other rigidly by connecting members in an advantageous manner and serve for simultaneously striking the three movable contact members 39. However, they may also be not coupled and act independently of each other on the respective movable contact member 39 associated with them.

What is claimed is:

1. An automatic switch comprising the combination of a latching mechanism having an unlatching lever and a movable contact member which can be actuated by the latching mechanismand a magnetic tripping device comprising, l

a first armature mechanically linkedto said unlatcha second armature mechanically linked to said movable contact member,

a magnetic core, a

an exciter coil causing magnetic flux to flow between said magnetic core and said first armature across a first air gap and causing magnetic flux to flow be- I tween said magnetic core and said second armature across a second air gap, wherein said first armature is placed at least in part in the same magnetic flux path as is said second armature, and

magnetic shunt means for magnetically bridging said second air gapat least in part with said magnetic core. v

2. The automatic switch of claim 1 wherein said magnetic shunt means bridging said second air gap becomes magnetically saturated at a current through said exciter .coil within the tolerance range for the response current of the first armature.

3. The automatic switch of claim 1 wherein said first air gap is less than said second air gap when said magnetic tripping device is in quiescent condition with no flux n 4. The automatic switch of claim 1 wherein both of said first andsecond armatures are plunger armatures.

' 5. The automatic switch of claim 4 wherein said first plunger armature is coaxially placed within said second armature. v

6. The automaticiswitch of claim 4 wherein said second plunger armature is coaxially placed within said first plunger armature.

9. The automatic switch of claim 1 wherein said second armature is aplunge'r type armature nested cylindrically within a magnetic shunt comprising a hollow cylinder of magnetic material magnetically connected to said magnetic core.

10. The automatic switch of claim 9 wherein said first armature is abar of magnetic material hinged to'a magnetic yoke.

l 1. The automatic switch of claim 1 wherein said second armature is a plunger-type armature and said magnetic shunt means is an elongated bar magnetically connected to said magnetic core placed coaxially within a hole in said second armature.

12. The automatic switch of claim 11 wherein said first armature is a plate of magnetic material constrained to move within a guide.

l 13. A three-phase automatic switch comprising the combination of a single latching mechanism having three separate unlatching levers all coupled with each other at 'a common restraining device, and three corresponding separate movable contact members which can be actuated by the latching mechanism, and three separate magnetic tripping devices comprising,

a first armature for each separate tripping device each mechanically linked to a separate unlatching lever, a second armature for each separate tripping device each mechanically linked to said corresponding movable contact members,

a magnetic core for each separate tripping device,

an exciter coil for each triggering device for causing magnetic .flux to flow betweensaid magnetic core and said first armature across a first air gap and causing magnetic flux'to flowfbetween said magnetic core and said second armature across a second air gap, wherein said first armature is placed at least in part in the same magnetic flux path as is said second armature, and s V I magnetic shunt means for magnetically bridging each said second air gap at least in part with each said magnetic core.

' a: if 

1. An automatic switch comprising the combination of a latching mechanism having an unlatching lever and a movable contact member which can be actuated by the latching mechanism and a magnetic tripping device comprising, a first armature mechanically linked to said unlatching lever, a second armature mechanically linked to said movable contact member, a magnetic core, an exciter coil causing magnetic flux to flow between said magnetic core and said first armature across a first air gap and causing magnetic flux to flow between said magnetic core and said second armature across a second air gap, wherein said first armature is placed at least in part in the same magnetic flux path as is said second armature, and magnetic shunt means for magnetically bridging said second air gap at least in part with said magnetic core.
 2. The automatic switch of claim 1 wherein said magnetic shunt means bridging said second air gap becomes magnetically saturated at a current through said exciter coil within the tolerance range for the response current of the first armature.
 3. The automatic switch of claim 1 wherein said first air gap is less than said second air gap when said magnetic tripping device is in quiescent condition with no flux flowing.
 4. The automatic switch of claim 1 wherein both of said first and second armatures are plunger armatures.
 5. The automatic switch of claim 4 wherein said first plunger armature is coaxially placed within said second armature.
 6. The automatic switch of claim 4 wherein said second plunger armature is coaxially placed within said first plunger armature.
 7. The automatic switch of claim 1 wherein said magnetic shunt means is formed by said first armature.
 8. The automatic switch of claim 1 wherein said magnetic shunt is a hollow cylinder of magnetic material.
 9. The automatic switch of claim 1 wherein said second armature is a plunger type armature nested cylindrically within a magnetic shunt comprising a hollow cylinder of magnetic material magnetically connected to said magnetic core.
 10. The automatic switch of claim 9 wherein said first armature is a bar of magnetic material hinged to a magnetic yoke.
 11. The automatic switch of claim 1 wherein said second armature is a plunger-type armature and said magnetic shunt means is an elongated bar magnetically connected to said magnetic core placed coaxially within a hole in said second armature.
 12. The automatic switch of claim 11 wherein said first armature is a plate of magnetic material constrained to move within a guide.
 13. A three-phase automatic switch comprising the combination of a single latching mechanism having three separate unlatching levers all coupled with each other at a common restraining device, and three corresponding separate movable contact members which can be actuated by the latching mechanism, and three separate magnetic tripping devices comprising, a first armature for each separate tripping device each mechanically linked to a separate unlatching lever, a second armature for each separate tripping device each mechanically linked to said corresponding movable contact members, a magnetic core for each separate tripping device, an exciter coil for each triggering device for causing magnetic flux to flow between said magnetic core and said first armature across a first air gap and causing magnetic flux to flow between said magnetic core and said second armature across a second air gap, wherein said first armature is placed at least in part in the same magnetic flux path as is said second armature, and magnetic shunt means for magnetically bridging each said second air gap at least in part with each said magnetic core. 